Duke University researchers gathered 16 wild-born bonobos from the Lola Ya Bonobo sanctuary in the Democratic Republic of Congo and led them one at a time into one of two adjacent rooms divided by a fence. On the opposite side of the fence from where the bonobos were was an apple hanging by a rope. The dangling fruit was clearly visible to the bonobos, but inaccessible.

Unless, that is, they climbed the fence and released a pin that would allow the apple to drop within reach of any nearby bonobos. If there were other bonobos in the room, a bonobo was four times more likely to climb the fence and release the apple than if the room was empty. They didn't even need to be asked by another bonobo to do it.

Another study published in April 2018 further illustrates that bonobos will share food with strangers. In that study, two different groups of bonobos were observed in the wild sharing a carcass. "Solicitation involved behaviours such as peering and stretched out hands but no aggression or forceful taking. As in other cases, the transfer of food from the male to females was passive," said lead researcher Barbara Fruth.

However, sharing between bonobos may only involve food according to a September 2018 study. Researchers observed bonobos shared nuts with each other but not the tools they used to open the nuts. They also noted that bonobos were unique from chimpanzees because they voluntarily shared food. Chimps were less passive, only allowing others to take food from them or sharing after another chimp aggressively begged.

This degree of altruism in the bonobos may be unconscious. In another experiment, 21 bonobos watched videos of other familiar bonobos yawning or making other natural expressions or they saw videos of bonobos from the Columbus Zoo doing the same actions. The yawns of unknown bonobos were just as contagious as those of the known bonobos. Researchers aren't sure if this just an empathetic response or a social nicety, but it does indicate that bonobos have a positive response to complete strangers.

The researchers conclude that much of this behavior is likely an evolutionary trait. When they reach adulthood, female bonobos leave their original group to find a new one. Being nice to new bonobos — like getting and giving food without being asked — can help a bonobo be accepted into a new group. Basically, bonobos like to make a good first impression, and being kind is an excellent first step.

Editor's note: This article has been updated since it was originally published in November 2017.